Finding the column number of the smallest element in a certain row

Question

Using R

Say for example you have a matrix such as the one below.

    > C<-matrix(c(0,-7,2,8,0,0,3,7,0,3,0,3,0,0,0,0),nrow=4,byrow=TRUE)
> C
         


        

Answer 1

If there is only a single minimum for each row you can find it with

apply(C, 1, which.min)

or (from R: finding column with minimum value in each row when there is a tied). See ?max.col for more options.

max.col(-C, "first")

edit (thanks to @flodel in the comments)

You can do this for individual rows by

which.min(C[1,])

Or if there are multiple matches

apply(C, 1, function(i) which(i == min(i)))

You get 5, as -7 is the fifth element of the matrix as it goes column wise. Look at c(C)